The CAN bus is a differential bus system that places high demands on signal symmetrization. In this context, the better the signal symmetrization, the lower the radio-frequency interference radiation and the interference at a subscriber station, such as for example a car radio. The opposite-phase signals CAN_H and CAN_L must be controlled in such a way that their mean value deviates as little as possible from center voltage VCC5/2=2.5V.
Currently, the signal symmetrization is achieved in that the resistances of the switches to ground GND and to the potential VCC5 are balanced in such a way that, in the dominant bus state, or dominant state of the bus, in which the difference voltage of the signals CAN_H−CAN_L has a value of approximately 2V, the mean value voltage is 2.5V. The balancing of the switch resistances takes place for example through suitable dimensioning or via regulating circuits described, for example, in German Patent Application No. DE 10250576 A1.
However, problems occur in the switching edges, because the driver stages for CAN_H and CAN_L have different delay times. These delays are a function of process conditions and of temperature, and are subject to aging. Thus, a fixed runtime compensation can achieve only an incomplete reduction of interference peaks in the mean value voltage.